Action of Caerulein on Gastric Secretion in Man

GASTROENTEitOLOC.'i

Vol. 59, No. r, Printed ifl lJ. S. A .

Copyright © 1970 by The Williams & Wilkins Co.

ACTION OF CAERULEIN ON GASTRIC SECRETION IN MAN ANDHEA AGOSTI ,

Gwuo

M.D.,

BEiri'ACC INI ,

STE FANO BIASIOLI,

M.D. ,

AND

M.D., Pu.D.

Institute of Pharmacology, University of Parma , Parma , Italy

Caerulein was tested for its stimulant activity on gastric acid secretion on 47 healthy subjects. The threshold stimulant dose was 0.05 to 0.10 Jtg per kg by the intramuscular route. The maximal dose tolerated with no side effects was 0.75 !lg per kg. With 1 llg per kg, f1ush, tachycardia, and nausea, lasting a few minutes, were observed. The maximal peak acid output with caerulein (0.5 J.Lg per kg) was 3.7 ± 0.6 milliequivalents per 15 min, approximately one-half of that obtained with pentagastrin (6 J.Lg per kg). It is concluded that in man, as had previously been shown in dog, caerulein is a partial agonist in stimulating gastric secretion and may be used as an antagonist of the secretion elicited by pentagastrin. Caerulein, a decapeptide amide isolated from the Australian amphibian Hyla caerulea, bears a close structural similarity to the COOH-terminal part of cholecystokinin and gastrin. In a preliminary investigation,' caerulein was shown to stimulate gastric secretion in man even at very low doses. It seemed worthwhile to amplify these first results in order to clarify this interesting activity and to compare the effects of caerulein with those of pentagastrin.

juice. Both juices were aspirated by continuous manual aspiration with glass syringes. Caerulein was injected in doses of 0.05, 0.1 , 0.25, 0.5, 0.75, and 1 11g per kg of body weigh t intramuscularly. E ach dose was administered to a group of 7 subjects. In 5 subjects, gastric acid secretion was studied immediately following administration of caerulein (0.5 l'g per kg intramuscularly) and 1 week following administration of pentagastrin (6 l'g per kg intramuscularly). This dose of pentagastrin has been shown to produce a maximal response in man. " Two 15-min basal collections were taken before the injection , and four 15-min collections were taken after the injection . Gastric juice, divided into 15-min samples, was measured to the nearest milliliter. Duodenal juice was aspirated and discarded. Acid concentration was determined by titrating 5-ml samples to pH 7.0 with 0.1 N NaOH with the u se of an automatic titra tor (Autoburet, Radiometer , Copenhagen, Denmark). Acid output was expressed in milliequivalents per 15 min . Subjects were placed in semireclining positions to obtain optimal gastric aspiration. Pure caerulein (compound marked F.I. 6934, molecular weight 1352) was kindly supplied by Farmitalia Laboratories for Basic Research, Mila n, Italy. Pentagastrin was a gift from Dr. Morton Grossman, Los Angeles, California.

Methods Gastric secretory tests were carried out on 47 male subjects, ages 24 to 65 years, without gastric disease demonstrated by X-rays . After a 12-hr fast, a 16-Rusch double lumen tube was passed into the duodenum to a distance of 80 to 90 em from the nares. It allowed separate collection of gastric and duodenal Received, March 25, 1970. Accepted, May 13, 1970.

Address requests for reprints to: Dr. Giulio Bertaccini, Institute of Pharmacology, Ospedale Maggiore, 43100 Parma, Italy. This work was supported by a grant from the Consiglio Nazionale delle Ricerche, Rome, Italy. The authors wish to thank Dr. Morton I. Grossman and Dr. Marvin A. Brooks, Veterans Administration Hospital, Los Angeles, California, for their suggestions and the interest they have taken in the Present investigation.

Results Volume and acid output. The threshold stimulant dose of caerulein administered 727

728

AGOSTI ET AL.

intramuscularly was 0.05 to 0.1 11g per kg. The magnitude of the gastric response was proportional to the dose up to 0.5 f.lg per kg. With higher doses, no further increments of secretory response were observed (fig. 1). The pattern of secretory responses to different doses of caerulein is shown in figure 2. Secretion rose to a peak in the second or third 15-min period in 70% of the subjects, then declined, but maintained levels higher than basal for 1 hr or more (fig. 2). Although the magnitude of the response was dependent on the dose, the time of appearance of the peak response was not. In 5 subjects out of 7, within 10 to 15 min after injection of 1 11 g per kg of caerulein, facial flush, mild tachycardia, sweating, and nausea, lasting approximately 15 min, appeared. In only 1 subject, however, were the symptoms severe enough to warrant stopping the test. He was replaced by another volunteer, so that also this dose (1 11 g per kg) could be tested on 7 subjects. Comparison between caeruleir. and pentagastrin. The highest mean output in response to caerulein (0.5 11g per kg) and pentagastrin (6 11 g per kg) occurred in the second or third 15-min period in all the tests and then decreased rapidly. The

O~r--.-----.----,-----,

0.1

0.5

0.75

1

Caerulein dose, pg/kg FIG. 1. Ordiruzte, peak acid output expressed in milliequivalents per 15 min . Abscissa, doses in 11 g per kg. Each point represents the mean of the values obtained from 7 subjects. Vertical bars, standard errors.

Vol. 59, No . .'i

5 c:

E 1/)

~ w

4

E 3

:::J

a.

:; 2 0 "0

0

<(

1

-1

0

1

2

3

4

15 min periods

FIG. 2. Ordina te , acid output in milliequivalents per 15 min. Abscissa, time in 15-min periods. From top to bottom , 0.50, 0.25, 0.10, and 0.05 11g per kg of caerulein. (Each dose was administered to a group of 7 subjects.)

peak 15-min output, without regard to the time after injection, was 3.7 ± 0.6 milliequivalents following administration of caerulein and 8.4 ± 1.0 milliequivalents following administration of pentagastrin. The difference was highly significant (P < 0.02). Contamination of gastric juice with bile as a consequence of reflux from duodenum to stomach was minimized by continuous aspiration of gastric and duodenal juice. However, in order to have an idea of the degree of reflux of alkaline duodenal content into the stomach, the maximal acid concentration obtained following caerulein was compared with that obtained after pentagastrin, which has no cholecystokinetic effect. Mean peak acid concentration was 94 ± 12 milliequivalents per liter after caerulein and 109 ± 13 milliequivalents p er liter after pentagastrin. Thus, the difference in the response be· tween the two stimulant agents was attributable mainly to change in volume of secretion. The peak 15-min acid output after caerulein was 32 to 59% of the peak 15-min acid output after pentagastrin (fig. 3). Discussion As repeatedly stated by many authors, '1-7 caerulein shares the COOH-terminal pentapeptide with gastrin and cho-

November 1970

ACTfON OF CAERULEIN ON GASTR!C SECRETJON

c: 10

E 11'1

~ w

E

::J

Q.

::J

5

0

~

., 0

.,

.lO:

CD Q.

SUBJECTS FIG. 3. Compa rison between caerulcin 0.50 !Jg per kg (black columns) and pentagastrin 6 !Jg per kg (whzte columns) in 5 subjects. Ordinate, peak acid output in milliequiva lents per 15 min .

lec~s~o.kin in

and possesses many of the of these peptides. As regards gastnc secretion, striking quantitative differences were observed in different animal species. Bertaccini et a!.' found caerulein to be 7 to 30 times as potent as gastrin I in the rat. These results were confirmed by Sewing and Albinus, " who were able to establish a dose-response relation for synthetic human gastrin I and caerulein, and who calculated that caerulein was, on a molar basis, 45 times more active than gastrin I. Pesente and Erspamer (unpublished data) showed that caerulein greatly increased the active transport of chloride in the isolated gastric mucosa of R~na esculenta; in this test, human gastrm I was at least 500 times less active than caerulein on a weight basis. Bertaccini et a\. 4 found the activity of caerulein to be 1.8 times as high as that of gastrin I in dogs with Heidenhain's pouches. These results were obtained by comparing the activities of the two peptides after subcutaneous administration of doses 2 to 4 times as high as the threshold stimulant dose. Stening and Grossman" had different results in gastric fistula dogs, but with different experimental conditions. Giving the two peptides by continuous intravenous infusion, they were able to establish clear dose-response lines. They found that the relative potency of gastrin I and caeacbv~t1es

729

rulein could not be accurately estimated because the dose-response lines were not parallel. Moreover, they observed that the threshold molar dose of caerulein was lower than that for gastrin, but the maximal levels attainable with caerulein were lower than with gastrin . In the present experiments, different doses of caerulein were administered to different subjects and, of course, this may decrease the reliability of the data obtain~d. Ho.wever, the maximal response obtamed after 0.5 11 g per kg of caeru lein (considered th e maximal dose for this peptide) was about one-half of the maxi~al response obtained with pentagastrin m the same subjects. This according to Grossman,!' may signify th~t caerulein is only a partial agonist as regards gastric secretion. Because it is a partial agonist caerulein is not appropriate for routin~ testing of human gastric function. In this respect, caerulein behaved like cholecystokinin-pancreozymin, which was observed by Wormsley 10 to be considerably less powerful than pentagastrin in stim~­ lating human gastric secretion . Since both caerulein and cholecystokinin-pancreozymin have the same COOH-terminal pentapeptide of gastrin, they may occupy the same receptors as gastrin and, therefore, act as antagonists of pentagastrin- or gastrin-mediated acid secretion . The inhibition of pentagastrin-evoked gastric secretion by caerulein was observed by Stening et a!. 1 1 in dogs and by Brooks ~t a!.'~ in man. Of course, caerulein is not an ideal inhibitor, as it possesses an evident intrinsic stimulant action . An extensive investigation is in pro~-,rress in this Institute directed to find a caerulein analogue endowed with sufficient affinity for the gastric receptors to act as an inhibitor of gastrin , and at the same time devoid of intrins ic activity or ability to excite the receptors. REFERENCES 1. Agosti A, Biasioli S, Na ranjo G: Azione della

cacruleina sulla secrezione gastrica umana. Boll Soc Ttal Bioi Sper 45:778-781 , 1969 2. A Multicentre Pilot Study: Pen tagastrin as a

730

3.

4.

5.

6.

7.

8.

AGOSTI ET AL.

stimulant of maximal gastric acid response in man. Lancet 1:291-295, 1967 Bertaccini G, De Caro G, Endean R, et al: The actions of caerulein on the smooth muscle of the gastrointestinal tract and the bladder. Brit J Pharmacol34:291-310, 1968 Bertaccini G, Endean R, Erspamer V, et al: The actions of caerulein on gastric secretion of the dog and the rat. Brit J Pharmacol 34:311-329, 1968 Bertaccini G, Braibanti T, Uva F: Cholecystokinetic activity of the new peptide caerulein in man. Gastroenterology 56:862-867, 1969 Stening GF, Grossman MI: Gastrin-related peptides as stimulants of pancreatic and gastric secretion. Amer J Physiol217:262-266, 1969 Bertaccini G, De Caro G, Endean R, et al: The action of caerulein on pancreatic secretion of the dog and biliary secretion of the dog and the rat. Brit J Pharmacal 37:185-197, 1969 Sewing F, Albinus M: Effect of gastrin I and

9.

10.

11.

12.

Vol. 59, No. 5

caerulein on gastric acid secretion in rats. ,J Pharm Pharmacal 21:58-59, 1969 Grossman MI: Effect of gastrin, cholecystokinin and secretin on gastric and pancreatic secretion: a theory of interaction of hormones, Proceedings of the Symposium on Origin, Chemistry, Phy. siology, and Pathophysiology of Gastrointestinal Hormones, Wiesbaden . Munich, Schattauer Verlag, 1969 Worm sley KG: Gastric response to secretin and pancreozymin in man. Scand J Gastroent 3:632636, 1968 Stening GF, Johnson LR, Grossman MI: Effect of cholecystokinin and caerulein on gastrin- and histamine-evoked gastric secretion. Gastroenter· ology 57:4-1- 50, 1969 Brooks AM, Agosti A, Bertaccini G, et al: Inhibi· tion of gastric acid secretion in man by peptide analogues of cholecystokinin. New Eng J Med 282:535- 538, 1970